Characteristics and uses of JFE443CT ferritic stainless steel

JFE has developed high corrosion resistance ferritic stainless steel JFE443CT to replace SUS304. The developed steel has the same corrosion resistance as SUS304 and is not affected by price fluctuations due to the absence of Ni and Mo elements. As an alternative to SUS304, developed steel has been widely used in kitchenware, building materials, electrical equipment, automobiles, and other fields.

Once. Introduction

In the field of household goods and home appliances, SUS430 is mostly used from an economic point of view; in the automotive field, new steel grades for multiple purposes have been developed, and most of the ferritic stainless steel is used. In the fields of building materials and industrial machinery, steel is required to have good corrosion resistance, workability and weldability, and high versatility. From the results of years of use, SUS304 is mainly used.

Although SUS304 steel has excellent performance, its main raw material nickel is a rare metal, and its selling price fluctuates drastically. Therefore, JFE has developed a ferritic stainless steel JFE443CT (21Cr-0.4Cu-0.3Ti) to replace SUS304.

The developed steel has the following characteristics:

(1) It has the same excellent corrosion resistance as SUS304;

(2) It is not affected by price fluctuations because it does not add Ni and Mo;

(3) It has the same formability as the original ferritic stainless steel.

Since the characteristics of the developed steel are very different from those of SUS304, it is important to accurately grasp its characteristics to determine the use and utilization of technology. This article briefly introduces the characteristics and representative uses of the developed steel.

Second, the characteristics of JFE443CT

1. Basic characteristics

The chemical composition of JFE443CT steel is shown in Table 1:

Table 1: Representative chemical composition of JFE443CT (%)

It can be seen from the data in the table that the developed steel increased the Cr content to 21% while also adding 0.4% Cu to ensure the same corrosion resistance as SUS304; and 0.3% was added as a stabilizing element The Ti, the residual C, N in the steel into harmless Ti (C, N), that is, titanium carbonitrides, thereby improving the corrosion resistance and workability of the welded part.

The mechanical properties of JFE443CT are shown in Table 2. The r-value in the table (ie, the Lankford value) is the ratio of the logarithmic strain in the width direction to the logarithmic strain in the thickness direction when the steel plate is strained (referred to as the plastic strain ratio of the steel plate). The larger the value, the better the deep drawing performance of the steel plate.

Compared with SUS304, the developed steel is soft, so it has a high R-value and excellent workability. In addition, compared with SUS304, although the elongation rate of the developed steel is lower (60% for the former and 31% for the latter), and the protruding processability is poor, its r-value is high, so the deep drawing performance is excellent. Therefore, when using developed steel to form, the deep drawing should be carried out rather than the protruding process.

Table 2: Mechanical properties of JFE443CT (representative values)

The developed steel is as magnetic as SUS430, and has a smaller thermal expansion coefficient than SUS304, and has excellent thermal conductivity. Its physical properties are shown in Table 3.

Table 3: Physical characteristics of JFE443CT (representative values)

2. Weldability

The developed steel reduces the impurity elements C and N in the steel, and at the same time adds the stabilizing element Ti, so the welded joint has excellent corrosion resistance and mechanical properties.

In order to ensure good mechanical properties and corrosion resistance, the following points must be noted for the welding of developed steel.

(1) Welding between different types of stainless steel: If TIG butt welding is carried out between the developed steel and SUS304, which has a higher C content, the resulting sensitization will reduce the corrosion resistance of the welded joint. Therefore, it is not suitable to use SUS304 with C content ≤0.08％, generally 0.05％～0.06％, but SUS304L (18Cr-9Ni, C≤0.03％).

(2) Welding wire: In order to prevent the corrosion resistance of the welded joint from being reduced due to sensitization, the use of Y308 series (component 0.05C-20Cr-10Ni) welding wire should be avoided, and Y308L series with low C content (component 0.02 C-20Cr-14Ni) and Y309L series (composition 0.02C-23Cr14Ni) welding wire.

(3) Shielding gas: In order to prevent oxidation and C infiltration (of the welding part), a sufficient amount of argon protection should be provided not only from the surface of the welding workpiece but also from the inside.

(4) Appropriate input heat: Compared with SUS304, the necessary input heat when developing steel welding has increased, but it should be noted that as the input heat increases, the grains of the welding part will increase, which may reduce its toughness.

Both the same material welding part of JFE443CT and the welding part with SUS304 have sufficient strength and ductility. Moreover, as shown in Table 3, compared with SUS304, the developed steel has a lower thermal expansion coefficient and a higher thermal conductivity, which has the advantage that it is difficult to produce welding deformation.

3, finishing materials, 2BW finishing materials

In addition to the 2B (annealing and pickling) material and BA (bright annealing) material with the surface finishing of general stainless steel, the developed steel is also equipped with high-productivity (tandem-CAL) finishing products.

The 2B finishing material of the developed steel is shiny, but it is different from the white SUS304 2B finishing material. On the 2B finishing material of the developed steel, there may be small defects that need to be repaired during processing, or the anti-glare property is poor And other issues so targeted the development of a new white surface 2BW finishing material.

The relative index and picture comparison show that the brightness and whiteness of JFE443CT’s 2BW finishing material are the same as that of SUS304’s 2B finishing material, with a low-gloss white appearance. When the developed steel and SUS304 2B finishing materials are used in combination, the color difference of the 2BW finishing materials can be reduced.

4. Wrinkle resistance

In the beginning, the steel developed under this development sometimes experienced severe wrinkling, but due to the optimization of the processing and production conditions, its wrinkle resistance was successfully improved. For example, the results of measuring the wrinkle resistance of steel by 20% stretching show that the JFE443CT steel before the improvement has a corrugation height of 4 ¦Ìm, and the corrugation height after the improvement is reduced to about 1.5 ¦Ìm.

Three, outdoor use

1. The salt spray test results with JFE443CT and SUS304, SUS430, and hot-dip galvanized steel sheet show that after 672h test of the general galvanized sheet (the coating amount is 62g/m2), the galvanized layer loses its anti-rust function and rusts. After the 2000h test, the steel plate rusted completely; even the steel plate with the thick galvanized layer (the coating amount is 527g/m2) rusted after the 2000h test and rusted after 5000h. SUS430 rusted from the end after 168h test. Contrary to the above-mentioned situation, JFE443CT and SUS304 did not rust even after the 5000h test and had excellent corrosion resistance.

In addition, a three-month exposure and corrosion resistance test of the simulated air-conditioning channel of developed steel and SUS304 trial-produced was carried out at a place 10m away from the seawall in Chiba Beach. The results show that the corrosion of the developed steel is slight, showing the possibility of replacing SUS304.

As mentioned above, the developed steel has sufficient corrosion resistance for outdoor use, and it has begun to replace SUS304 as various building materials, construction tools, metal accessories, household goods for outdoor use, and industrial machinery.

2. Indoor use

In indoor home appliances and household products, the use of SUS304 has also been replaced with developed steel, such as cookware pots, incubators, refrigerators, and kitchen cabinets.

As shown in Table 3, the developed steel is magnetic and has high thermal conductivity. If it is used in an induction cooker, the heating speed is fast and the energy consumption is saved (when adding the same amount to the round developed steel and the SUS304 pot Water, under the same heating conditions, the former will boil water 30 minutes faster than the latter).